Field of the Invention
The present invention is broadly concerned with improved anti-corrosion products for use with heavy brines employed in the petroleum industry during well drilling. More particularly, the invention is concerned with such products and corresponding methods wherein corrosion inhibitors comprising amounts of a phosphonate or salts thereof, and gluconic acid or salts thereof, are introduced into the brines. The combined ingredients of the inhibitors are synergistically effective in reducing corrosion rates attributable to the brines.
Description of the Prior Art
Calcium chloride and calcium nitrate brines are used in establishing and maintaining petroleum (i.e., oil and gas) wells. For example, calcium chloride brines are used in drilling muds to cool and lubricate well bits and to remove cuttings from the hole. The brines help maintain the consistency of the drilling muds and add density thereto, to better enable the muds to overcome formation pressures and thereby oil, gas, and water in place. Such brines also inhibit clay and shale hydration and add needed weight to the muds.
Brines are also used as completion fluids just before the producing formation is reached, to flush the hole clean of solids so that the casing can be cemented in place. As clear, substantially solid-free brines, calcium chloride and calcium nitrate brines are ideal as completion fluids.
Once a well casing is cemented in place, smaller diameter tubing is inserted in the casing, which makes the flow of oil or gas more efficient and can be replaced if plugs develop. Tubing in used with packer fluid that keeps the well fluids away from the casing to minimize corrosion. Calcium chloride and calcium nitrate brines are used in the packing injected into the annular space between the tubing and the casing in order to maintain pressure levels.
Finally, these brines can also be used as workover fluids, by flushing wells free of solids before they are repaired, or before reworking a well that has been idle.
Notwithstanding the multiple uses of these brines, problems remain. A principal drawback is the fact that the brines tend to be highly corrosive to downhole equipment surfaces, causing pitting and erosion thereof often with the result that the equipment in question must be repaired or replaced at frequent intervals.
Attempts have been made to control the corrosive activity of well brines, see e.g., U.S. Pat. No. 4,784,778. This patent teaches that particular thio compounds and aldose group antioxidants may be used in the context of zinc halide-based, high density fluids. U.S. Pat. No. 5,171,460 describes scale inhibitors for use with calcium and similar brines, comprising a phosphonomethylated oxyalkyleneamine. Other background references include U.S. Pat. Nos. 4,061,589, 4,279,768, 4,303,568, 4,849,171, 4,869,827, 5,330,683, 5,589,106, 5,023,011, and 7,172,677, and PCT Publications Nos. WO 86/04634 and WO 2008/084503. However, no fully satisfactory anti-corrosion system for calcium chloride and calcium nitrate brines has heretofore been developed.